1. Field of the Invention
The present invention relates to a signature verification system, a communication device, a verification device, a signature generation method, and a signature verification method.
2. Description of the Related Art
Hitherto, it has been known that a digital signature and a digital certificate for verifying the digital signature are given to recorded electronic data in order to certify that the electronic data is not altered. The digital signature is also simply referred to as a “signature”, and the digital certificate is also simply referred to as a “certificate”.
For example, Japanese Patent Unexamined Publication No. 9-305661 discloses a source authentication method in which two devices authenticate the source of electronic data by using the respective certificates signed by the same certificate authority, as a method of verifying the effectiveness of electronic data.
For example, Japanese Patent Unexamined Publication No. 2005-252318 discloses the following electronic certificate effectiveness confirmation system as a system for verifying a signature given to electronic data. In the electronic certificate effectiveness confirmation system, a transmission source of the electronic data obtains effectiveness confirmation information from a certificate authority as a third party other than the transmission source and a transmission destination of the electronic data, and transmits the effectiveness confirmation information to the transmission destination of the electronic data.
In techniques disclosed in Japanese Patent Unexamined Publication No. 9-305661 and Japanese Patent Unexamined Publication No. 2005-252318, it is difficult to verify the validity of the signature attached to the electronic data at a low cost.